This invention relates to a method and apparatus for controlling a manipulator so as to enable the manipulator to reproduce faithfully and simply the motions of the human arm, for example.
In recent years, automation of machine tool and assembly machines has vastly increased. Performance of simple work by use of simple programs has already found wide acceptance. In contrast, the development of a robot of complicated mechanism which may well be called the ultimate aim in machine automation has made no appreciable progress. One of the obstacles that stand in the way of this development is the fact that the processing of given data inevitably necessitates use of a large-scale electronic processing system supported by complicate programs. As an inevitable consequence, systems currently available for the purpose produce motions at slow response and involve more energy loss than is reasonably acceptable. None of the systems developed to date meets the desired use satisfactory. In other words, materialization of highly efficient electronic circuitry or a simpler, more efficient way of carrying out data processing programs needed for the control can alone further the possibility that the motions produced by the human arms, for example, will be reproduced faithfully at quick response by use of machines. While the present invention will be described in connection with a manipulator adapted to provide effective reproduction of the motions of the human arm, it will be clearly understood by those skilled in the art that the control can be effectively applied to the reproduction of the motions of the other parts of the human body as well.
The human arm contains joints one each at the wrist, the elbow and the shoulder. The motions of the human arm involve seven degrees of freedom, namely, the combinations of the longitudinal and lateral motions of the wrist, the twisting (rotary) motion of the forearm, the flexing motion of the elbow, the twisting (rotary) motion of the brachium, and the combinations of the longitudinal and lateral motions of the shoulder. This means that reproduction of the motions of the human arm by the operation of a manipulator requires at least a total of seven axes of rotation. Generally, the manipulator can be oriented for the control of the reproduction of these motions by feeding to each of these axes of rotation necessary command signals which represent angular magnitudes of motions to be calculated in accordance with the data on the coordinates of all positions and the angular values of all directions that can be possibly assumed by the arm. For the optimization of this control, it is definitely necessary to use an arithmetic unit which permits highly complicated programs involving the arithmetic operations of trigonometric functions, inverse trigonometric functions and matrices and incorporates a huge memory circuitry.
As regards the system touched upon above, the invention titled "Method for control of multi-joint type manipulator" published in Japanese Laid-open Patent Publication No. 98867/1976 has offered some improvement in and concerning the complicated arithmetic operations to be performed on a real-time basis. To be specific, this method comprises dividing the whole area covered by all possible motions of the manipulator hand into sections resembling those of lattices, calculating in advance the angles which are assumed by the joints of the arm on given lattice points as the hand is posed on such lattice points, and storing the data consequently obtained in a memory unit, on condition that data on the angles of the joints falling at intermediate points of the aforementioned lattice sections are calculated by means of interpolation. This method has the merit of relieving the arithmetic unit of the arithmetic operations of trigonometric functions which have heretofore consumed the greater part of the time required for the real-time processing of data. While this method permits a fairly large cut in the time required for data processing, it nevertheless necessitates use of an arithmetic unit possessing a huge memory capacity for storing comprehensive data covering all the motions that can be produced by the manipulator hand in the prescribed area. Worse still, this method suffers from inferior accuracy of data calculation because it relies on calculations which make use of lattice points and interpolation. This method lacks practical feasibility and is merely experimental.
An object of this invention is to provide a method for controlling a manipulator by simple operations involving, as the objective-command values, the coordinates indicating the positions of the hand, the Euler's angles indicating the directions of the hand, and the angles of rotation of the elbow for thereby enabling the mechanisms of the manipulator capable of rotating and moving the joints and the whole arm of the manipulator to reproduce the motions of the human arm faithfully in rapid response, and an apparatus for effecting the aforementioned control of the manipulator mechanisms without necessitating any large memory capacity.